Car control unit: the ECU, its function, parts, breakdowns and reprogramming

Abbreviations ECU mean Electronic Control Unit, Unidad de Control Electrónico in Spanish, and is also often called car control unit. On more than one occasion it has been compared to the brain of the vehicle, although here we are going to try to be a little more exact.

What is ECU

The ECU or control unit is a computer that centralizes all engine information, with which makes decisions and adapts its functioning to each circumstance. It controls components as important as the fuel injection, plugs, the pressure of turbo and EGR valve, the fans of the refrigeration system, etc. In addition, it allows the engine to perform practically the same, regardless of the atmospheric pressure or temperature (to give some basic examples).

However, today one cannot speak of a single “brain” since there are several specialized ECUs in each part of the car. Although normally, when we talk about the ECU or dry control unit, we are talking about the one that deals with the engine and some other functions.

El rest of switchboards have been appearing take some weight off the main ECU, due to the large amount of calculations that need to be done in modern cars. These can be: one dedicated to Stability control, another for the airbags and other security functions, for the instrument panel, for the doors, mirrors and windows, seats, etc. They can be so many some cars have almost 100Although most are simple and small.

What function does the switchboard of a car have?

The control units or ECUs are in charge of orchestrating all the related elements of the car. In the past, motors worked without electronicsWhich did not allow them to adapt so well to different working conditions. Now the engine control unit takes into account factors such as air pressure, temperature, the position of the camshaft, the crankshaft and the butterfly, the exhaust gases, the revolutions and a long etcetera of data.

In addition to it also records everything that happens in the engine that is out of the ordinary. So the mechanics will only have to connect to it through a diagnosis machine to read the recorded data and see what is wrong with the motor.

In short, the operation of a car switchboard can be divided into:

Receive input data: The control unit receives data from the different sensors and detectors that it has connected. In the case of the motor, they will be, for example, the revolution sensors, the sensors of the crankshaft and camshaft position, air flow sensor or the sensors of crankshaft.
perform calculations: the switchboard uses all the data to make the decisions it has programmed. That's why you need a certain processability so that your decision making is very fast. This is very important for the proper functioning of the engine. For example if crank knock is detected, you have to decide to shut down the engine or go into limp mode very quickly to avoid damage.
send out signals: the switchboard send the signals appropriate for the actuators to work how it's requeired. For example: increase fuel injection to prevent the car from stalling if the revs drop too low (hence the typical jerks). The actuators located in the brakes that allow the ESP or the EGR valve to be activated, which opens or closes depending on the detected exhaust gases, are also good examples.
Stores information: each malfunction or abnormal data They are stored in the engine control unit. For example, a turbo pressure sensor, which indicates that the turbo is not blowing with the expected force. Data that can be read if we connect to the control unit through an OBD connection.

Loss of car power: causes and solutions

Parts of a car control unit

In order to do all this, the car's control unit or ECU has a large number of parts in one Printed circuit board. With what resembles a computer like the one we use at home or at work, although without a conventional hard drive, as well as specific processors and memories for its task. These parts are:

input interface: where it receives all the signals coming from the different sensors and converts the digital signals for understanding by the CPU.
output interface: which converts the digital signals from the control unit and its CPU so that they are understandable by the sensors and actuators of the engine or other devices controlled by the control unit.
Central Processing Unit (CPU): is the processor or processors that receive the data, perform the calculations and send a response based on the program. They are used to control the engine, traction control systems, electronic braking systems, automatic transmissions, and everything else that the ECU manages. As we have told you before, in many cases each system has its switchboard.
storage memories:
- Memory of only reading (ROM): which has the basic information
- Programmable memory (eeprom / Flash): this information can be changed. This type of memory is the one that is manipulated when reprogramming a switchboard or cloning it if it has broken down.
- Random access memory (RAM): This is temporary data that is used as required and can be written and rewritten many times. Just like on a conventional computer.
Fuente de alimentación: It is the part that supplies energy to the entire switchboard and regulates the electric current.
other electronic components: here you will find everything you need to supply power to the control unit and keep it stable, coordinate its components and protect the control unit. Therefore, within this section we find, for example, the following:
- capacitors: which are mainly found in the power supply, but also in some areas of the control unit to maintain a stable voltage inside it and in the sensors with which it communicates.
- diodes: that allow current to flow in one direction but not in another to protect the control unit
- Drivers: with which, for example, the ignition coils on the spark plugs are controlled
- Watches or crystals: that regulate the speed at which the instructions are executed in the processor or processors and synchronize them with the rest of the components of the control unit.

Car control unit faults

The control units are very protected inside the vehicle, so it is not common for them to break down. Even so, when they break down it is usually for two main reasons:

Humidity in the car control unit

In this case the damage can be difficult to repair. The same thing that happens when any complex electronic device gets wet. That is why many times it is exchanged for a second-hand one if there is one and the information from the damaged control unit is cloned. Although damaged elements can also be repaired.

The most common water damage inside the switchboard are:

damaged power supply: which means changing various components within it.
In addition, humidity can mean that they appear weld spots with oxide corrosion at various points in the switchboard.

voltage rise or fall

As you have seen in the section on the parts of the control unit, it is full of capacitors and other security measures to keep the voltage stable within the circuit. However, in some circumstances the capabilities of these can be exceeded and end up damaging something. In these cases the most common faults are:

the regulatory systems themselves, such as condensers or capacitors. For example, capacitors damaged by the voltage spike or that have lost their condensing capacity over time. It may also have been damaged diode.
It can also happen that some solder point of the circuit to crack due to excess current. What it means to weld it.
burnt track: which are usually solved by making external jumpers to the printed circuit board. For example, soldering a fine wire on the burnt track that acts as a conductor
damaged transistor: It may be a damaged output transistor or a damaged 5V regulator transistor. In which case you have to replace them with new ones.

Price to repair the car switchboard

In the event that your switchboard has broken down the price of repair It depends a lot on the model: between 500 and 1.500 euros. At best it might just be some minor component of it that is easily repaired. Another case is that you have to clone your switchboard information to a second-hand one. What it means to extract the information and use a programmer to put it in the new one or directly solder the memories of your control unit in the replacement one (if they have not been damaged).

In the worst case, you have to put a new switchboard for not having second hand. What in many cases can be around prices of between 1.000 and 3.000 euros depending on the car for which it has to be obtained. Luckily, the car's control unit is an element that is rarely damaged throughout the useful life of the car.

Reprogramming of the control unit or ECU

With everything we have seen so far, you can imagine that since the control unit is the one that manages the engine and its components, it is the key to increase power and torque delivery. Indeed, the reprogramming consists of the engine receiving more demanding orders. What happens is that This can be done in several ways and not all have the same price or have the same reliability. The types of reprogramming and their prices are:

Chip the engine (chip power)

It is about changing the memories of the control unit of your engine with a different programming. It is the same thing that is done when cloning a switchboard (soldering and desoldering memories). The new Flash memories, EEPROM or the one that has been necessary to change have a programming and maps that demand more power and torque from the engine.

Its price depends on the model and the place you go to (always go to professionals), but it ranges between 400 and 700 euros.

power switchboard

It is about placing a second control unit between the engine and the factory control unit. In such a way that the data received by the car's control unit are falsified by the one we add. The result is that once again the engine ends up receiving orders demanding more performance.

Reprogramming of the switchboard

Here it comes to literally reprogram the switchboard, neither chipped nor secondary switchboards. That is, delete the programming of your control unit and put a new one in the one that is configured for more power. However, there are two ways to do it:

Reprogramming using a computer: This allows the professional to see what state the car is in and do a personalized reprogramming. What, if done well, allows reaching the most secure configuration and the best performance according to each client. Between 300 and 1.500 euros.
Reprogramming via PPC: It is a device that connects through the OBD socket. Here there is no contribution of value according to the state of your engine. Simply copy the information that is in your control unit to make a backup copy and record the new one with the standard maps that the engine reprogramming takes to obtain more power.

Reprogram the car, what does it offer us? We tested it in a Fiat Grande Punto

How to connect to the car control unit

To do this you simply need a OBD Diagnostic Scanner or Machine. With it you will be able to see the information that has been saved in its memory. As we have told you in the section on the functions of the control unit: the failures registered by it and the status of each component of the car.

Its price is usually between 15 and 40 euros. Although there are much more expensive ones that have many more functions. Some examples of OBD scanners are those of LAUNCH, those of EDIAG (the most recommended) or those of ANCEL.

Images – Nenad Stojkovic, Tim Geers, Klaus Nahr, endolith, 3ndymion, Albertas Agejevas

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